Spoilage potential of psychrotrophic bacteria isolated from raw milk and the thermo-stability of their enzymes / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

The storage and transportation of raw milk at low temperatures promote the growth of psychrotrophic bacteria and the production of thermo-stable enzymes, which pose great threats to the quality and shelf-life of dairy products. Though many studies have been carried out on the spoilage potential of psychrotrophic bacteria and the thermo-stabilities of the enzymes they produce, further detailed studies are needed to devise an effective strategy to avoid dairy spoilage. The purpose of this study was to explore the spoilage potential of psychrotrophic bacteria from Chinese raw milk samples at both room temperature (28 °C) and refrigerated temperature (7 °C). Species of Yersinia, Pseudomonas, Serratia, and Chryseobacterium showed high proteolytic activity. The highest proteolytic activity was shown by Yersinia intermedia followed by Pseudomonas fluorescens (d). Lipolytic activity was high in isolates of Acinetobacter, and the highest in Acinetobacter guillouiae. Certain isolates showed positive β-galactosidase and phospholipase activity. Strains belonging to the same species sometimes showed markedly different phenotypic characteristics. Proteases and lipases produced by psychrotrophic bacteria retained activity after heat treatment at 70, 80, or 90 °C, and proteases appeared to be more heat-stable than lipases. For these reasons, thermo-stable spoilage enzymes produced by a high number of psychrotrophic bacterial isolates from raw milk are of major concern to the dairy industry. The results of this study provide valuable data about the spoilage potential of bacterial strains in raw milk and the thermal resistance of the enzymes they produce.

Multiplicação microbiana no leite cru armazenado em tanques de expansão direta / Microbial multiplication in raw milk stored in direct expansion bulk tanks

O presente estudo objetivou avaliar o efeito do tempo de armazenagem do leite em tanques de expansão direta, modelo de duas e quatro ordenhas, sobre a contagem bacteriana total (CBT) e a contagem de bactérias psicrotróficas (CBP). As avaliações foram conduzidas em 19 propriedades leiteiras, localizadas nas regiões Serrana e Oeste de Santa Catarina, as quais utilizavam equipamentos de refrigeração do leite por expansão direta, modelo de duas ou quatro ordenhas, com taxa de ocupação variando de 60 a 100% de sua capacidade. Antes e após cada ordenha, foram coletadas amostras de leite para análise de CBT, CBP e contagem de células somáticas (CCS), totalizando aproximadamente 36 horas de armazenagem (quatro ordenhas). O tempo de armazenagem do leite cru resfriado não afetou a CBT e CBP (P>0,05) em ambos os modelos. O modelo de tanque de expansão afetou somente a CBP (P<0,05), com média inferior para amostras de leite de tanques de duas ordenhas em relação ao de quatro ordenhas (3,61±0,104 e 4,00±0,120UFC mL-1 (log10), respectivamente). Conclui-se que tanques de resfriamento por expansão direta, utilizados dentro de suas especificações quanto ao volume de leite a ser resfriado, permitem a manutenção da CBT e da CBP em sistemas de transporte do leite ao laticínio a cada 48 horas.

The purpose of this study was to evaluate the effect of the cold storage period of raw milk in bulk tanks, using two and four milking models, on total bacterial count (TBC) and psychrotrophic bacterial count (PBC). A total of 19 dairy farms, located in West and Uplands of the Santa Catarina State - Brazil, was been evaluated. Each dairy farm had direct expansion bulk milk tank and an occupancy rate varying from 60% to 100%. Samples were collected before and after each milking procedure to determine PBC and TBC, totalizing four milking and a storage period of 36 hours. The storage time did not affect TBC and PBC (P>0.05). The bulk tank model only affected the PBC (P < 0.05), with two-milking model presenting a lower mean than four-milking model (3.61±0.104 and 4.00±0.120CFU mL-1 (log10)). It was possible to conclude that bulk tanks, when used properly concerning raw milk volume to be chilled, allow the TBC and PBC to remain stable in the transportation systems of raw milk to the industry each 48 hours.

Detection of airborne psychrotrophic bacteria and fungi in food storage refrigerators

The purpose of this study was to determine the microbiological air quality (psychrotrophic bacteria and airborne fungi) and distribution of fungi in different types of ready-to-eat (RTE) food-storage refrigerators (n=48) at selected retail stores in the city of Edirne, Turkey. Refrigerators were categorized according to the type of RTE food-storage: meat products, vegetables, desserts, or a mix of food types. Microbiological quality of air samples was evaluated by using a Mas-100 Eco Air Sampler. Four refrigerators (all containing meat products, 8.3%) produced air samples with undetectable microorganisms. The highest detected mean value of airborne psychrotrophic bacteria and fungi was 82.3 CFU/m³ and 54.6 CFU/m³, respectively and were found in mixed-food refrigerators. The dominant airborne fungal genera found were Penicillium (29.0%), Aspergillus (12.0%), Mucor (9%), Cladosporium (8%), Botyrtis (7%), and Acremonium (6%). By definition, RTE food does not undergo a final treatment to ensure its safety prior to consumption. Therefore, ensuring a clean storage environment for these foods is important to prevent food-borne disease and other health risks.

Association between milking practices and psychrotrophic bacterial counts in bulk tank milk / Asociación entre prácticas de ordeño y recuento de organismos psicrótrofos en leche de tanque de frío

The objective of this work was to determine on-farm risk factors for psychrotrophic bacterial counts in bulk tank milk from dairy farms in Argentina. Raw milk samples from bulk tanks of 27 dairy farms were examined for total psychrotrophic counts (TPC), proteolytic psychrotrophic counts (PPC) and lipolytic psychrotrophic counts (LPC) (dependent or outcome variables). A survey recording infrastructure conditions, milking equipment and milking management (independent variables) was performed. Bivariate association proofs and logistic regression analyses were used to determine association between independent variables and psychrotrophic bacterial counts. Milk cooled in plate heat exchangers or barrel tanks were 16.39 and 10.52 times more likely to yield TPC and PPC above the standard established for high quality milk compared with milk cooled in bulk tanks, respectively. Periodic cleaning of cooling tanks (3 times a week or daily) was associated with lower TPC (approximately 1.5 log CFU/ml) than weekly cleaning frequency and farms where milkers did not wash their hands during milking time were 7.81 times more likely to have higher PPC. No association was found between LPC and any of the independent variables. The only variable associated with TPC and PPC in a logistic regression model was the refrigeration system used on the farm. Dairy farms that possessed bulk milk cooling tanks yielded the lowest bacterial counts. Results of this study highlight the importance of both the type of cooling system used on the farm and its adequate hygienic maintenance for obtaining low pshychrotrophic counts at dairy farm.

El objetivo del trabajo fue determinar los factores de riesgo para altos recuentos de organismos psicrótrofos en leche de tanques de tambos de la Argentina. Se examinaron muestras de leche cruda de tanques de frío de 27 tambos, y se realizó el recuento de organismos psicrótrofos totales (PT), de psicrótrofos proteolíticos (PP) y de psicrótrofos lipolíticos (PL) (variables dependientes). Se realizó una encuesta para registrar las condiciones de infraestructura, el equipo de ordeño y las prácticas de ordeño (variables independientes). Se utilizaron pruebas bivariadas de asociación y regresión logística para determinar la asociación entre las variables independientes y los recuentos de organismos psicrótrofos. La leche enfriada en sistemas de placas de intercambio o tanques tipo cuba tuvo una probabilidad mayor de dar recuentos elevados de PT y PP (16,39 y 10,52) comparada con la enfriada en tanques tipo "panza fría". La limpieza periódica del equipo de frío (3 veces por semana o diariamente) se asoció con bajos recuentos de PT (aproximadamente 1,5 log de UFC/ml). Los tambos cuyos ordeñadores no se higienizaban las manos durante el ordeño tuvieron una probabilidad 7,81 veces mayor de tener recuentos elevados de PP. No se encontró asociación entre el recuento de PL y las variables independientes. La única variable asociada con los recuentos de PT y PP en el modelo de regresión logística fue el sistema de enfriamiento utilizado en el tambo. El tipo de sistema de refrigeración usado y su adecuado mantenimiento higiénico son importantes para la obtención de leche con baja carga de organismos psicrótrofos en el tambo.

Screening of Psychrotrophic Bacteria and Their Application to Treatment of Livestock Wastewater / 微生物学通报

Fourteen psychrotrophic bacteria were isolated from swamp soil collected in Ruoergai plateau wetland,and their generation time and degrading ability of livestock wastewater CODcr was determined.The results showed that the generation time was within 4.9 h to 11.6 h.Based on the generation time,9 psychro-trophic strains(NLJ1,NLJ6,NLJ7,NLJ9,NLJ10,NLJ11,NLJ12,NLJ13 and NLJ14),whose generation time was within 4.9 h to 5.6 h,were chosen to treat livestock wastewater.The results suggested that these 9 strains had different CODcr disposal ability when treating livestock wastewater singly at 6?C for 6 h,and strains NLJ6,NLJ7,NLJ9,NLJ10,NLJ11 and NLJ13 had good ability to degrade livestock wastewater,the CODcr degrading rate was about 60%~70%,hence,they were used as high efficient strains;However,the CODcr degrading rate of the other strains was less than 50%.After inoculating mixture culture of these six strains into the distilled livestock wastewater,after 6 h's treating,the CODcr degrading rate reached to 85.42%.Furthermore,activated sludge collected from Yaan,Dujiangyan and Chengdu were inoculated by the mixture culture of those six strains,and used to treat livestock wastewater for 6 h.The results showed that the average CODcr degrading rate was 81.67%,76.32% and 70.56%,respectively;Variance analysis showed that there was no significant differentiation between each treatment,which revealed that those six psychrotrophic strains had good adaptability to different source of activated sludge.